In emergency situations, such as man-made and natural disasters, wireless networks are often overloaded, and unable to service all communication requests. Overloading can occur on contention-based access channels used for requesting traffic channel assignments, as well as on traffic channels. This is particularly problematic for emergency personnel, such as police and fire departments who rely upon the ability to communicate with each other to effectively respond to the emergency situation. For this reason many emergency agencies employ private wireless networks that are not accessible by the general public. These private wireless networks are expensive to maintain, and frequently cannot interoperate with each other. For example, a police agency may employ one type of private wireless network that does not allow communication with a fire agency that employs a different type of private wireless network.
FIG. 1 is a flow diagram of a conventional method of communicating with a wireless network. The method of FIG. 1 is described in connection with a CDMA-based network known as Evolution Data-Only (EV-DO) Revision A, (also referred to as a DOrA network). Like all wireless networks, DOrA networks encounter problems with access channel congestion and traffic channel congestion.
A mobile station monitors an overhead or control channel and reads system parameters broadcast over this channel (step 105). When the mobile station desires the ability to transmit information to the wireless network, the mobile station requests a universal access terminal identifier (UATI) (step 110). This request is sent over a contention-based access channel, and when more than one mobile station transmits a request at any particular time on this channel the requests can collide such that neither request is received by the network.
Under normal operating conditions the mobile station then receives a UATI assignment on a control channel (step 115) and transmits a request for a traffic channel over the access channel (step 120). When there are available traffic channels, then the mobile station receives a traffic channel assignment message over a control channel (step 125). The traffic channel assignment sent from the network includes a medium access control identifier (MAC ID). MAC ID's are only valid for the time that the traffic channel assignment is in effect, and the DOrA system can support 114 MAC IDs at a time with each sector and carrier. If more than 114 mobile stations are requesting connections in any particular sector and carrier, then the system will have to either reject the request or close another users connection. The assigned traffic channel is dedicated to the requesting mobile station.
The mobile station then negotiates session protocols with the wireless network, which also authenticates the mobile station (step 130). The session protocols are basically configurations that will be used when exchanging user data. The system authentication (e.g., using the AN-AAA and CHAP challenge and response) verifies that the user device has a legitimate subscription with the service provider. When this EVDO session is completely established, the user (via applications on the mobile station) can proceed to setup a PPP session (including user authentication) with the PDSN and activate various data applications (which could include voice services).
After the mobile station has been authenticated, a traffic channel is assigned to the mobile station (step 135). As long as the mobile station continues to transmit some information over the assigned traffic channel during a predetermined period of time (“No” path out of decision step 140), then the wireless network will maintain the traffic channel assignment with the mobile station (step 135).
When the mobile station does not send any information over the assigned traffic channel for a predetermined period of time (“Yes” path out of decision step 140), then the wireless network tears down the traffic channel and de-assigns the MAC ID (step 145), which can then be reassigned. Even though the DO connection has been torn down, the DO and PPP sessions remain open for a long time (the default session timer for a DO session is set to 54 hours.) Accordingly, the wireless network determines whether it has received a request to establish a DO connection from the mobile station (step 150). When the wireless network receives such a request (“Yes” path out of decision step 150), then the mobile station receives a traffic channel over a control channel (step 125). This technique is commonly referred to as the “fast connection method” because a mobile station maintains UATI, DO session and PPP session assignments. With the DO session still open, if the mobile station wants to send more data, it must first request another DO connection, which it must do via the common access channel. In this case however, the message on the access channel will be ‘signed’ and the system can easily validate the device/user without detailed authentication.
When the wireless network does not receive a request to reestablish a DO session or an associated PPP session after a predetermined amount of time (“No” path out of decision step 150 and “Yes” path out of decision step 155), then the wireless network deletes the DO and PPP sessions for the mobile station (step 160). For ease of explanation, FIG. 1 illustrates a single period of time being employed in step 155 for determining whether to delete the DO and PPP sessions. However, those skilled in the art will recognize that different periods of time can be employed for deleting DO and PPP sessions.
In EV-DO systems, there is a limited amount of forward and reverse traffic channel capacity to be shared among users. The design of the forward link traffic channels is such that users in better RF signal conditions can be served at a higher data rate than users with poor RF signal conditions. This can be leveraged to maximize the total amount of data that can be sent through the sector. However, it is also desirable to serve all users, not only those in good coverage conditions. Therefore, a scheduling algorithm is employed which attempts to balance these needs. All data is treated in a ‘best effort’ manner, with no assurance of reliability, particular data rate etc. Further, in DOrA there is no mechanism to reserve any of resources for particular users' exclusive use.
Enhancements have been made in DOrA to distinguish traffic types, and to reserve resources to serve some traffic types over others. This is called intra-user QoS, and prioritizes some types of traffic (or ‘flows’) over others for each user. Additionally, mechanisms can be employed to prioritize one user's data over another user's data (i.e., inter-user QoS). When a user requests and is authorized to use a particular type of data traffic, the system reserves resources to support that traffic. The system manages its total resource allocations and will refuse to grant more resources when it has no more available to grant.